For those who do not realize it, Twitter allows porn. How do i know?
I started to gain followers, sweet (or should that be tweet?) young things offering me the rented usage of certain of their body parts. I was miffed and checked back on who was following them and waddyaknow? Porn sites and private user accounts filled with images that you would not want your kids to find.
From what i have seen it is the individual that must block access. There appears no recourse for reporting a site other than for spam and Twitters own rules forbid pornographic content in profiles or backgrounds but otherwise anything goes.

Suggest that those with youngsters that use the service have a long hard think about it.